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Soil & soil fertility Africa Soil Health Consortium 2014 Lecture 2: Introduction to soil and soil fertility

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Soil & soil fertility. Africa Soil Health Consortium 2014. Lecture 2: Introduction to soil and soil fertility. Objectives. Gain knowlegde on the principles underpinning ISFM practises Introduction to soil Soil texture Porosity Mineral fraction Organic matter Introduction to nutrients - PowerPoint PPT Presentation

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Page 1: Soil & soil fertility

Soil & soil fertility

Africa Soil Health Consortium

2014

Lecture 2: Introduction to soil and soil fertility

Page 2: Soil & soil fertility

ObjectivesGain knowlegde on the principles underpinning ISFM practises

•Introduction to soil– Soil texture– Porosity– Mineral fraction– Organic matter

•Introduction to nutrients– Understanding the function of nutrients in plant growth– Recognizing nutrient deficiencies

•Soil fertility– Understanding the concept of soil fertility– Introduction to soil fertility management– Conservation agriculture & organic agriculture– Minimizing losses of added nutrients

Page 3: Soil & soil fertility

Soil

Soil s

olids

Pore space

+ soil fauna and flora

Pore space: -space for roots and micro-organisms-air for micro-organisms-water storage

Mineral fraction:-Provides support to plant roots-Slowly releases nutrients into the soil solution

Organic fraction:-Soil organic matter (SOM)-Key issue in soil fertility management

Page 4: Soil & soil fertility

Pore space

Porosity: volume of the soil occupied by air and the soil solution

Porosity inWell-drained moist soil: sufficient moisture for plant growth and sufficient aeration for proper root functionDry soil: all pores are filled with air drought stressFlooded soil: pores are saturated with water roots cannot breathe and plants may die

Illustration adapted from Brady 1984, The nature and properties of soils, 9th edition.

Soil particle

Water film

Air space

mm0 0.5 1.0 1.5 2.0 2.5

Page 5: Soil & soil fertility

Mineral fraction

Sand: 0.05 - 2.0 mmSilt: 0.002 - 0.05 mmClay: < 0.002 mm

Illustration adapted from: www.iconn.org

SiltClay

mm0 1 2 3 4 5

Sand

Page 6: Soil & soil fertility

Clay % Silt %

Sand %

Mineral fraction

Page 7: Soil & soil fertility

Mineral fractionThe finger test

Page 8: Soil & soil fertility

Mineral fraction & PorositySoil texture affects-Porosity-Water holding capacity-Nutrient retention and supply-Drainage-Nutrient leaching

Illustrations adapted from: http://wegc203116.uni-graz.at/meted/hydro/basic/Runoff/print_version/04-soilproperties.htm

Pore Space in Sandy Soil vs. Clay Soil

Sandy soil Clay soil

Larger pores Smaller

poresLess total pore

volume =

Less porosity

Greater total pore volume

=Greater porosity

Infiltration Variations by Soil Texture

Sand Silt Clay

Page 9: Soil & soil fertility

Mineral fraction & CECCations: positively charged ions (e.g. K+, NH4

+)

Cation exchange capacity (CEC): the maximum quantity of total cations that a soil is capable of holding. Clay fraction and SOM: Small particle size Large negatively charged surface area More positions to hold cations High CEC

Illistration adapted from: http://www.spectrumanalytic.com/support/library/ff/CEC_BpH_and_percent_sat.htm

H+

Ca2+

Mg2+

NH4+

Na+

K+

H+K+H+H+

Sand

Clay

Clay – Many positions to hold cations

Sand– Few positions to hold cations

Page 10: Soil & soil fertility

Mineral fraction & CECCEC depends on-Clay content-Type of clay mineral-SOM content-Soil pH

Clay minerals differ in structure•1:1 clay minerals

– CEC varies with soil pH – Found in most upland soils in SSA

•2:1 clay minerals – Large inherent CEC capacity – Found in fertile lowland soils

Illustration adapted from Lory ‘Structure of Clays’ www.soilsurveys.org

Page 11: Soil & soil fertility

Organic fraction: SOMSOM: plant and animal residues, in various stages of decompisition

Picture: http://www.guiadejardineria.com/jardineria/suelos-y-abonos/page/7/

Page 12: Soil & soil fertility

Organic fraction: SOM

- Contains essential plant nutrients- Improves the soil’s Cation Exchange

Capacity - Improves the soil’s water-holding capacity

(SOM can hold up to five times its own weight in water!)

- Improves water infiltration - Buffers soil pH- Binds with toxic elements in the soil- Improves soil structure by stimulating

activity of soil flora and fauna- Regulates the rates and amounts of

nutrients released for plant uptake

SOM is a key issue in soil fertility management!

Illustration adapted from: http://www.tekura.school.nz/departments/horticulture/ht106_p4.html

Top soil

Sub soil

% Organic matterLitter layer 4321 5

Organic matter

Page 13: Soil & soil fertility

Soil analysis

• Soil test: chemical method for estimating the nutrient-supplying power of a soil

• Laboratory needs a representative composite sample of 0.5 kg

• Be aware of heterogeneity within fields when sampling!

Page 14: Soil & soil fertility

Guidelines for soil sampling

Take a representative sample!!!

1.Check the area to be sampled for notable features (e.g. slope, soil types, vegetation, drainage).2.Draw a sketch map, and identify and mark the location of sampling sites.3.Take soil samples with a soil auger at the sampling depth (0-20 cm or 20-40 cm).4.Take 10-35 sub-samples per site, the number depending on the size and heterogeneity of the field. 5.Combine the sub-samples to one composite per site and mix thoroughly. 6.If necessary, reduce sample weight by sub-dividing7.Label the sample of soil properly.8.Air-dry the sample and when dry, store it, properly labelled, in a plastic bag or a glass bottle for further analyses.

Page 15: Soil & soil fertility

NutrientsMacronutrients: at least 0.1% of plant dry matter per macronutrient

Nitrogen (N): -Amino acid/Protein formation-Photosynthesis

Phosphorus (P):-Energy storage/transfer-Root growth-Crop maturity-Straw strength-Disease resistance-Needed in large amounts during plant growth-Required for N2-fixation by legumes

Potassium (K):-Plant turgor pressure maintenance-Accumulation and transport of the products of plant metabolism-Disease resistance-Required for N2-fixation by legumes

Sulphur (S):-Part of amino acids (protein formation)-Synthesis of chlorophyll and some vitamins-Required for N2-fixation by legumes

Magnesium (Mg):-Photosynthesis-Activates enzymes-Carbohydrate transport

Calcium (Ca):-Cell growth and walls -Activates enzymes (protein formation and carbohydrate transfer)-Essential in ‘calcicole’ plants (e.g. Groundnut) for seed production.-Influences water movement, cell growth and division-Required for uptake of N and other minerals

Poor mobility

Very mobile

Very mobile

Very mobile

Very mobile

Quite poor mobility

Very

mob

ile

Very mobile

Poor

mob

ility

Qui

te m

obile

Quite

poo

r mob

ility

Med

ium

mob

ility

Page 16: Soil & soil fertility

NutrientsMicronutrients: less than 0.1% of plant dry matter

Iron (Fe):-Photosyntheiss-Respiration

Manganese (Mn):-Photosynthesis-Enzyme function

Boron (B):-Development/growth of new cells

Zinc (Zn):-Nucleic acid synthesis and enzyme activation

Copper (Cu):-Chlorophyll formation-Seed formation-Protein synthesis

Molybdenum (Mo):-Protein synthesis and N uptake-N2-fixation by legumes

Chlorine (Cl):-Movement of water and solutes-Nutrient uptake-Photosynthesis-Early crop maturity-Disease control

Cobalt (Co):-N2-fixation by legumes

Nickel (Ni):-Required for enzyme urease

Sodium (Na):-Water movement and balance of minerals

Silicon (Si)-Cell walls-Protection against piercing by sucking insects-Leaf presentation-Heat and drought tolerance

Page 17: Soil & soil fertility

Nutrient deficiency

Healthy

N-deficient

P-deficient

K-deficient

Diseased

Page 18: Soil & soil fertility

Nutrient deficiencies

Page 19: Soil & soil fertility

Nutrient deficiency: exercise

Page 20: Soil & soil fertility

Nutrient deficiency: exercise

P-deficient-Stunted growth-Purplish colouring

K-deficient-Browning of leaf edges

Page 21: Soil & soil fertility

Nutrient uptake Nutrient Plants take upN NO3

-, NH4+

P H2PO4- , HPO4

2-

K K+

S SO42-

Mg Mg2+

Ca Ca2+

Fe Fe2+ and Fe3+

Mn Mn2+ and Mn3+

B (BO3)3-

Zn Zn2+

Cu Cu2+

Mo Mo42+

Cl Cl-

Co Co2+

Ni Ni2+

Na Na+

Si (SiO4)4-

Page 22: Soil & soil fertility

Nutrient availabilityReadily available- Nutrients from soluble fertilizers (e.g. KCL), readily mineralized SOM, nutrients held on the edges of soil particles, and in the soil solution

Slowly available- Nutrients in organic form, such as plant residues and organic manures (particularly with a high C/N ratio), slowly soluble mineral fertilizers (e.g. Phosphate rock) and the SOM fraction resistant to mineralization

Not available- Nutrients contained in rocks, or adsorbed on soil particles

Page 23: Soil & soil fertility

Soil fertilityThe capacity of soil to supply sufficient quantities and proportions of essential chemical elements (nutrients) and water required for optimal growth of specified plants as governed by the soil’s chemical, physical and biological attributes.

•Chemical elements for plant nutrition•Adequate soil volume for plant root development•Water and air for root development and growth•Anchorage for the plant structure

Inherent Dynamic

Soil texture Soil organic matter (SOM)

Depth Nutrient- and water-holding capacity

Parent material Soil structure

Page 24: Soil & soil fertility

Soil fertility management practices• Nutrient deficiencies prevent a good harvest• Nutrient deficiencies can be expressed during plant growth

• Use mineral (fertilizer) or organic (manure, crop residues) to supply nutrients

• Use special fertilizer blends containing micronutrients or manure in case of micronutrient deficiencies

Correcting nutrient deficiencies

Soil acidity correction

Breaking hardpans

Water harvesting

Erosion control

Land preparation

Planting date

Spacing

Planting practices

Weeding

Pest and disease management

Intercropping

Healthy N-deficient

P-deficient

K-deficient

Page 25: Soil & soil fertility

Soil fertility management practices

• Acidity is caused by– inherent soil properties– acidity inducing management (e.g. long-term use of ammonium

based fertilizer)

• Acid soils have high exchangeable Al (Al toxicity)

Correcting nutrient deficiencies

Soil acidity correction

Breaking hardpans

Water harvesting

Erosion control

Land preparation

Planting date

Spacing

Planting practices

Weeding

Pest and disease management

Intercropping

Lime•Increases pH•Prevents Al and Mn toxicity in acidic soils (pH <5.5)•Supplies Ca•Increases P and Mo availability•Can increase microbiological activity

•Apply lime to reduce exchangeable Al to +/- 15%

Page 26: Soil & soil fertility

Soil fertility management practices

• Compaction sub-surface soil barrier to root growth• Break hardpans by ploughing or chisel ploughing to 30 cm depth

Correcting nutrient deficiencies

Soil acidity correction

Breaking hardpans

Water harvesting

Erosion control

Land preparation

Planting date

Spacing

Planting practices

Weeding

Pest and disease management

Intercropping

Illustration adapted from: http://locallygerminated.wordpress.com/

Porous soil allows good root development

Sub-surface barrier to roots

Surface crust

Page 27: Soil & soil fertility

Soil fertility management practices

• Capture more rainfall in areas that are prone to drought– Harvesting additional water (e.g. Zaï)– Promoting infiltration by coversing the soil surface with mulch

• Labour intensive

Correcting nutrient deficiencies

Soil acidity correction

Breaking hardpans

Water harvesting

Erosion control

Land preparation

Planting date

Spacing

Planting practices

Weeding

Pest and disease management

Intercropping

Zaï pits in Niger Mulching of bananas, western UgandaPictures: fao.org

Lydia Wairegi
revised this from 'are' to 'include' in notes
Page 28: Soil & soil fertility

Soil fertility management practices

• Prone to erosion: fields on steep slopes, or on gentle slopes with course-textured top soil

• Measures: live barriers (e.g. grass strips), teracces, surface mulch

Correcting nutrient deficiencies

Soil acidity correction

Breaking hardpans

Water harvesting

Erosion control

Land preparation

Planting date

Spacing

Planting practices

Weeding

Pest and disease management

Intercropping

Bunds on sloping land in Burundi

Page 29: Soil & soil fertility

Soil fertility management practices

• Good seedbed preparation improves germination and reduces the chance for diseases

• A delay in planting date often affects yield negatively• Planting time is important especially when the growing

season is short

Correcting nutrient deficiencies

Soil acidity correction

Breaking hardpans

Water harvesting

Erosion control

Land preparation

Planting date

Spacing

Planting practices

Weeding

Pest and disease management

Intercropping

Page 30: Soil & soil fertility

Soil fertility management practices

• Crops compete for nutrients, water and light• Use a correct planting density, adjusted to crop type and the

environment. Consider the distance between rows, between plants within rows and the number of plants per planting hole.

Correcting nutrient deficiencies

Soil acidity correction

Breaking hardpans

Water harvesting

Erosion control

Land preparation

Planting date

Spacing

Planting practices

Weeding

Pest and disease management

Intercropping

Crop Optimal rainfall Poor rainfallDensity Between

rowsWithin rows

Density Between rows

Within rows

‘000 Plants/ha

cm cm ‘000 Plants/ha

cm Cm

Beans (common) 200 50 10 133 50 15

Maize 44 75 30 37 90 30

Soybean 444 45 5 333 60 5

Page 31: Soil & soil fertility

Soil fertility management practices

• Use viable seed (at least 80% germination)• Plant seeds at the correct depth and insert cuttings at correct angle• Plant more seeds than required for optimal plant density.

• Weeds compete with crops for nutrients, water and light.• Timely removal of weeds is essential• Weed before top dressing crop with fertilizer

• Control pests and diseases at specific growth stages

Correcting nutrient deficiencies

Soil acidity correction

Breaking hardpans

Water harvesting

Erosion control

Land preparation

Planting date

Spacing

Planting practices

Weeding

Pest and disease management

Intercropping

Delayed weeding reduces the crop response to fertilizer

Page 32: Soil & soil fertility

Soil fertility management practices

• Intercropping arrangements: take into account specific growth features and needs of individual crops to minimize intercrop competition.

• Examples: delayed planting of one intercrop, adjusting spacing, strip intercropping

Correcting nutrient deficiencies

Soil acidity correction

Breaking hardpans

Water harvesting

Erosion control

Land preparation

Planting date

Spacing

Planting practices

Weeding

Pest and disease management

Intercropping

Maize-pigeonpea Maize-cassava

Cassava-soybean

Page 33: Soil & soil fertility

Conservation agriculture (CA)Basic principles1.Soil disturbance is minimized by reduced or zero-tillage2.Use of at least 30% soil cover (mulch or cover crops)3.Use of crop rotations/associations

Advantages-Rapid planting of large areas-Reduction of soil erosion

Pitfalls-Competing uses of crop residues needed for mulch-Yields may decrease on the short-term (the increase often comes on the longer-term)-Increased weed pressure caused by reduced tillage-Full CA requires a fundamental change in the farming system. This may not be practical or enomic for the farmer-Possible decrease in agronomic efficiency of fertilizer use

Lydia Wairegi
revised 'agriculture'
Lydia Wairegi
'thus is underpinned' to 'this is underpinned'
Page 34: Soil & soil fertility

Organic agricultureReliance on organic resources to provide nutrients to sustain soil

fertility and produce economic crop yields

However, mineral fertilizers are an essential component in sustainable agriculture in SSA•Soil nutrients stocks in large parts of SSA have already become depleted and require replenishment•Organic resources are not available in large enough quantities to replenish and sustain nutrient stocks in the soil•Large and economic responses to mineral fertilizer are obtained in many parts of SSA•Organic resources are bulky and their management is labour intensive

ISFM: use of mineral fertilizer in combination with organic resources. The combination provides the greatest benefits!

Page 35: Soil & soil fertility

Minimizing losses of added nutrients

Losses of nutrients into the environment•Depletion of nutrients in farming systems• Eutrophication in case of excessive mineral fertilizer use (not common in

SSA)

Losses through•Harvesting crops recycling•Water and wind erosion•Leaching•Volatilization

Nitrogen is the most susceptible to losses•Very mobile, can be lost through different ways•NO3- is susceptible to leaching.

Page 36: Soil & soil fertility

Losses: Water and wind erosion

10 kg N/ha, 2 kg P/ha and 6 kg K/ha lost in low-input production systems in SSA

Measures: grass strips, stone rows, mulch layer, soil preparation methods (e.g. Zaï), improving SOM

Tied rigdes

Bunds on sloping land in Burundi

Page 37: Soil & soil fertility

Losses: Leaching

• Problematic in high rainfall areas and coarse-textured sandy soils (>35% sand)

• Mainly NO3- and exchangeable bases (K and Mg)

percolate beyond the reach of crop roots

Measures: • Improving soil structure to promote good root

development for increased accessibility of nutrients • Growing annual crops in association with trees, which

can ‘pump’ water and nutrients from deeper layers

Page 38: Soil & soil fertility

Losses: VolatilizationDenitrification of NO3

- •NO3

- N2O and N2 (gasses) •Occurs under anaerobic conditions Measures: improved soil drainage and maintain a good soil structure to avoid anaerobic growing conditions

Volatilization of NH3 in alkaline soils (high pH)Measures: deep placement of N-fertilizers

Volatilization of NH3 during storage and handling of manureMeasures: use anaerobic storage pits

Page 39: Soil & soil fertility

Summary

Porosity

CEC

Texture

Soil organic matter

Nutrients-Functions-Availability-Mobility-Deficiencies

Soil fertility management options

Conservation agriculture

Organic agriculture

Mimimizing losses of added nutrients-Erosion-Leaching-volatilization